1. Field of the Invention
This invention pertains to the field of diagnostic assays for detecting infection of an animal by the protozoan parasite Cryptosporidium, in particular, C. parvum. Also provided are novel C. parvum protein disulfide isomerase (PDI) polypeptides, and nucleic acids encoding the polypeptides.
2. Background
The Cryptosporidium parasites cause infection of a wide variety of animals, including birds, reptiles, and mammals. C. parvum is the principal pathogenic Cryptosporidium species in humans and domestic animals. C. parvum can cause acute diarrhea in hosts, although in immunocompetent hosts the disease is self-limiting (Wolfson et al. (1985) N. Engl. J. Med. 312: 1278–1282). In immunocompromised hosts (e.g., AIDS patients), C. parvum can cause a severe and potential lethal disease (Current et al. (1983) N. Engl. J. Med. 1252–1257; Pitlik et al. (1983) Arch. Intern. Med. 143: 2269–2275; Soave et al. (1984) Ann. Intern. Med. 100: 504–511).
Cryptosporidium infection typically results from ingestion of oocysts, which become excystated and release sporozoites. The sporozoites then infect gut epithelial cells. Once in the epithelial cells, the sporozoites mature into merozoites, which are released and infect additional epithelial cells. Cryptosporidium also has a sexual cycle, which also occurs in the gut epithelial cells and involves the production of sporulated oocysts. Some of the oocysts can become excysted before being shed from the cell. Both sporozoites and merozoites are found free in the gut.
Several Cryptosporidium sporozoite and merozoite surface antigen polypeptides have been reported. For example, five C. parvum surface antigens, genes encoding the antigens, and the production of antibodies against C. parvum are discussed in Peterson et al. (1992) Infect. Immun. 60: 2343–2348 and PCT patent application PCT/US93/05460 (International Publication No. WO 93/24649). Additional Cryptosporidium surface antigens, and production of anti-Cryptosporidium antibodies are discussed in, for example, Arrowood et al. (1989) Infect. Immun. 57: 2283–2288; Bjorneby et al. (1991) Infect. Immun. 59: 1172–1176; Bjorneby et al. (1990) J. Immunol. 145: 298–304; Lumb et al. (1989) Immunol. Cell Biol. 67: 267–270; Mead et al. (1988) J. Parasitol. 74: 135–143; Perryman et al. (1990) Infect. Immun. 58: 257–259; Riggs et al. (1989) J. Immunol. 143: 143: 1340–1345; Tilley et al. (1991) Infect. Immun. 59: 1002–1007; and Tilley et al. (1990) Can. J. Zool. 68: 1513–1519.
Diagnosis of Cryptosporidium infection has traditionally involved microscopic detection of ova and parasites (O&P) in stools, which is a laborious process. Other assays have used stains or fluorescent-labeled antibodies which are contacted with a sample, which is then examined under a microscope. Both of these assays, however, require subjective interpretation of results. More recently, antigen capture enzyme immunoassays have been described (e.g., Cypress Diagnostics “Cryptosporidium Ag”; Alexon ProSpecT Cryptosporidium Microplate Assay).
Therefore, a need exists for improved methods for detecting Cryptosporidium infection in animals, including humans. The present invention fulfills this and other needs.